<!DOCTYPE html>
<head>
<meta charset="utf-8">
<title>canvas</title>
<style type="text/css">
    *{
        margin: 0;
        padding: 0;
    }
    #canvas{
        border: 1px solid #000;
        background: #f7f7f7;
    }
</style>
</head>
<body>
    <canvas id='canvas' width="400" height="400">你的浏览器不支持canvas,请升级你的浏览器</canvas>
</body>
<script>
    
    var sun = new Image();
    var moon = new Image();
    var earth = new Image();
    function init(){
        sun.src = 'https://mdn.mozillademos.org/files/1456/Canvas_sun.png';
        moon.src = 'https://mdn.mozillademos.org/files/1443/Canvas_moon.png';
        earth.src = 'https://mdn.mozillademos.org/files/1429/Canvas_earth.png';
        window.requestAnimationFrame(draw);
    }

    function draw() {
        var ctx = document.getElementById('canvas').getContext('2d');

        ctx.globalCompositeOperation = 'destination-over';
        ctx.clearRect(0,0,300,300); // clear canvas

        ctx.fillStyle = 'rgba(0,0,0,0.4)';
        ctx.strokeStyle = 'rgba(0,153,255,0.4)';
        ctx.save();
        ctx.translate(150,150);

        // Earth
        var time = new Date();
        ctx.rotate( ((2*Math.PI)/60)*time.getSeconds() + ((2*Math.PI)/60000)*time.getMilliseconds() );
        ctx.translate(105,0);
        ctx.fillRect(0,-12,50,24); // Shadow
        ctx.drawImage(earth,-12,-12);

        // Moon
        ctx.save();
        ctx.rotate( ((2*Math.PI)/6)*time.getSeconds() + ((2*Math.PI)/6000)*time.getMilliseconds() );
        ctx.translate(0,28.5);
        ctx.drawImage(moon,-3.5,-3.5);
        ctx.restore();

        ctx.restore();
        
        ctx.beginPath();
        ctx.arc(150,150,105,0,Math.PI*2,false); // Earth orbit
        ctx.stroke();
        
        ctx.drawImage(sun,0,0,300,300);

        window.requestAnimationFrame(draw);
    }

    init();

</script>
</html>